Miniature motor assembly



March 21, 1967 H. W. WILKINSON MINIATURE MOTOR AS SEMBLY Original FiledOct. 5, 1960 4 Sheets-Sheet 1 F G. 2. n: 2e

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HARRY W. WILKINSON BY ATTOR NEY I March 1967 H. w. WILKINSON MINIATUREMOTOR ASSEMBLY Original Filed Oct. 5, 1960 4 Sheets-Sheet 2 INVENTOR.HARRY W. WILKINSON ATTORNEY r I M r 1967 H. w. WILKINSON MINIATURE MOTORASSEMBLY 4 Sheets-Sheet 3 Original Filed 001:. 5. 1960 JNVENTOR.

HARRY W. WILKINSON BY ATTOR N EY March 21, 1967 H. w. WILKINSON3,310,691

MINIATURE MOTOR ASSEMBLY Original Filed Oct. 5, 1960 4 Sheets-Sheet 4INVENTOR. HARRY W. WILKINSON FIG.

ATTORNEY h k United States Patent C) This is a division of my patentapplication Ser. No. 60,- 733 filed on Oct. 5, 1960, now Patent No.3,241,397, and is a continuation of application Ser. No. 450,830 filedApr. 26, 1965, now abandoned. v

This invention relates to gear heads, and more particularly concernsgear motors and precision gear heads having gears which are accuratelyaligned with a minimum of backlash and exceptionally low torque, and amethod 'of making such devices.

A gear motor is a combination of a gear head and a motor made as oneunit, or connected together to form one component.

In the synchro system of a computer, for example, there may be atransmitting synchro (not shown) electrically connected to an amplifier(not shown) which is connected by electrical connectors to a gear motor11. Motor 11 is connected to and actuates a receiving, synchro 55 tobring it into synchronism with the transmitting synchro.

All motors under consideration here are of the type which attain highspeed (on the order of ten thousand revolutions per minute, for example)under no load, but have low torque. If the end action of the system isto be accomplished in, for example, one minute, this means that theoutput shaft of the'gear, head must revolve one revolution in oneminute. Accordingly, with the input rotation at 10,000 rpm. and theoutput rotation at l r.p.m., the gear head accomplishes a speedreduction of ten thousand to one, with a corresponding increase oftorque.

If the time allotted for revolution of the output shaft of the gear headis only one-half minute, then the speed reduction of the gear head wouldhave to be five thousand to one, and the torque obtained on the gearhead output shaft would be one-half of the torque obtained from the tenthousand to one reduction.

If the time allotted for the revolution of the output shaft of the gearhead is not sufiicientto provide the desired torque, then a morepowerful motor must be used.

Accordingly, depending on the "requirements of the system, a gear headmay be designed to provide any desired torque to accomplish the functionneeded.

In such a system the object is to have the input (transmitter) and theoutput (receiver) in angular agreement, or as close thereto as possible.And it is the function of the motor, in response to the current supplied(via the amplifier) by the electrical difference between the transmitterand the receiver, to reduce the electrical and angular differencebetween the input and the output to as close to zero as possible with amechanical motion.

So that the smallest possible electrical differencebetween transmitterand receiver can be used with minimum of electrical amplification, themotor and the gear train assembly (gear head) should be able to rotatewith minimum of torque application.

It should be noted that the values of the gear reduction and backlashbetween the motor input and gear head output are determined by thesystem s'requirements.

The torque. required by the gear system to start and continue therotation of only theigear head (not considering the motor armature,etc.) is determined by: the. inertia of the elements (gears, shafts,bearings), the friction of and may become misaligned in use.

3,310,691 Patented Mar. 21, 1967 the bearings, and the engagement of thegears. The inertia of the gears is kept to lowest value by the physicaldesign of the gears (of such diameter as to have low inertia values),but the reduction of friction of the bearing and gears has heretoforenot been satisfactory because of the construction used for gear trainassemblies. A major problem presented is that of supporting the gearshafts in the gear head in such a manner as to prevent shaft deflectionand resulting binding of gears and bearings.

If the gear shaft is supported at only one end, even though supported bytwo spaced ball-bearing supports, the gear shaft bends and deflects asthe loaded gears tend to climb around each other, and so distort theircenters and introduce backlash characteristics into the system.

Conventional gear heads have two separate bearing plates connectedtogether and spaced apart by studs. In assembly, the individual gearshafts are located and assembled in one bearing plate, the other bearingplate is mounted over the other end of these assembled gear shafts, andthe bearing plates are connected together in spaced-apart relationshipby studs or screws.

Such bearing plates maybe misaligned in assembly, Any misalignment wearsone side of the gear teeth, and either causes the gears to bind, whereby'a great deal of unnecessary torque is required to turn the gears, orcauses the gears tospread and make backlash errors.

In gear heads constructed of separate bearing plates connected togetherand spaced apart by screws, if it is necessary to replace certain gearshafts and the gear head is taken apart to make such changes, thechances of putting it back together in proper alignment are very remote.Also, in the manufacture of such individual bearing plates, it is verydifiicult to maintain identical center locations and other dimensions onall plates. Even though the holes are bored while a number of plates areheld together in a cluster, in assembly of the motor the plate of onecluster is likely to be used with the plate of another cluster having adifferent center line.

Because of the high degree of accuracy required in synchro systems, thespecifications for gear heads require a minimum of backlash andexceptionally low torque. The use of a gear assembly with separatebearing plates spaced apart and connected by studs or screws, and theuse of gear shafts which are overhung (supported in. a

- cantilever fashion) have created backlash and gear friction andmisalignment errors.

To solve these problems, the present invention provides a gear cagewhich is integrally formed and carved from one piece of material.

However, the integral gear cage also presented a problem: of how toinsert the gear shafts since the overall length of the shafts exceedsthe distance between the inner faces of the gear-bearing bases of thecage. Logically, a long gear shaft cannot be put into a space too smallfor it.

The aforementioned problems have been solved by providing a gear cagewhich is integrally formed, and by inserting the end of the gear shaftinto one side of an opening in a gear-bearing base of the cage, andsupporting it therein a bearing which is inserted. into the opening fromthe other side of the base.

Accordingly, it is an object of this invention to provide a gear headwhich is so constructed that the gears are precisely positioned andremain so positioned during the entire life of the gear head.

It' is another object of this invention to provide a gear train whichhas minimum friction so that a minimum of torque movesit and theslightest voltage actuates' the gear train motor to rotate the gears.

It is another object to provide a gear head wherein the gear shafts aresupported on each side of the gear so as to eliminate any deflectioncaused by cantilever support of such gear shafts.

It is another object to prevent the misalignment of gear shafts causedby misalignment of gear-bearing plates.

It is another object of this invention to provide a gear head which maybe easily taken apart and put back together in proper alignment.

It is another object of this invention to provide a gear head and a gearmotor which are smaller and more compact than those previouslyobtainable.

It is another object to provide a gear head capable of giving very highgear reductions.

Other objects and advantages of this invention, including its simplicityand economy, and ease of manufacture on a mass production basis, willfurther become apparent hereinafter and in the drawings, in which:

FIG. 1 is a view in perspective of a gear motor constructed inaccordance with this invention;

FIG. 2 is a view in section taken as indicated by the lines and arrowsII--II which appear in FIG. 3;

FIG. 2a is a fragmentary view in section of another embodiment of theinvention;

FIG, 3 is a view in vertical section taken as indicated by the lines andarrows IIIIII which appear in FIG. 2;

FIG. 4 is a view in side elevation of another embodiment of theinvention; I

. FIG. 5 is a view in section of the embodiment of FIG. 4 taken asindicated by the lines and arrows V--V which appear in FIG. 6; 1

FIG. 6 is a view in vertical section taken as indicated by the lines andarrows VIVI which appear in FIG. 5;

FIG. 7 is a view in horizontal cross section taken as indicated by thelines and arrows VIIVII which appear in FIG. 6;

FIG. 8 is an exploded view in cross section showing how the individualgears are assembled in the gear cage;

FIG. 9 is a perspective view of a one-piece integrally formed gear cagewhich forms an element of this invention; and

FIG. 10 is a view in section of another embodiment of the invention.

Although specific terms are used in the following description forclarity, these terms are intended to refer only to the structure shownin the drawings and are not intended to define or limit the scope of theinvention.

Turning now to the specific embodiments of the invention selected forillustration in the drawings, there is shown a gear motor 11 comprisingan outer case 12, a

stator 13 positioned therein (and held by a cement layer 19) between abearing plate 14 and a bearing plate 15, a rotor 16 supported inbearings 17, 18 in plates 14, (the bearings 17, 18 being held in placeby snap-rings 21, 22), and a rotor shaft 23 having a tail shaft 24 atone end and a gear 25 at the other.

Also positioned in outer case 12 adjacent bearing plate 14 is anintegrally formed gear cage 26.

Gear cage 26 is screwed into the threads 27 of case 12. Bearing plates14 and 15 are properly centered and positioned in case 12 by positioningholes 28 which receive dimples 31 that are pressed into the outside ofthe case. Electrical leads 10 pass through an opening in end plate 15 toconnect with the wiring of stator 13.

Gear cage 26 includes a gear chamber 33 which is formed by inner base 34and intermediate base 35 connected together in spaced-apart relationshipby posts 36.

Gear cage 26 also includes another gear chamber 37 which is formedbetween intermediate base 35 and outer base 38.

Rotor shaft 23 extends into gear cage 26 through a clearance hole 41 inbase 34 and its gear 25 meshes with gear 42 on gear shaft 43. Pinion 44on shaft 43 actuates (through intermediate gearing not shown in FIG. 2but shown in FIG. 3) gear 45 on shaft 46, and pinion 47 on shaft 46 ispositioned within gear chamber 37 to mesh with output gear 48 of outputshaft 51. Gear 52 on shaft 51 meshes with gear 53 on rotor shaft 54 ofreceiving synchro 55.

Referring to FIG. 3, which shows the full gearing between gear 25 andgear 45, gear 25 drives gear 42 on shaft 43, pinion 44 on shaft 43drives gear 56 on shaft 57, pinion 58 on shaft 57 drives gear 61 onshaft 62, and pinion 63 on shaft 62 drives gear 45.

Referring again to FIG. 2, shaft 43 is supported in bearings 65, 66which are seated in aligned openings 67, 68. Snap-ring 71 in snap-ringgroove 72 holds bearing 65 in place, and snap-ring 73 in groove 74 holdsbearing 66.

Gear shaft 46 is supported in bearings 75, 76 which are seated inaligned openings 77, 78. Bearing 75 abuts against shoulder 81 of opening77, and bearing 76 is fixed in position by a snap-ring 82 in groove 83.

Shaft 51 is supported in bearings 84, 85 which are seated in alignedholes 86, 87. Bearing 85 abuts against shoulder 88 of hole 87, andbearing 84 is supported by a snap-ring 91 in groove 92.

FIGS. 4-9 show a modification of the present inven= tion wherein outercase 12 has been replaced by a dust cover 93 which covers a gear cage26a that is fastened to a standard motor 94 by bolts 95 (FIG. 7). Gearcage 26a is similar to gear cage 26, and has a base 34a which isprovided with a recess to receive the cap 97 of motor 94.

To construct the integral gear cage 26, chamber 33 is formed by taking asteel bar, cutting into the side of the bar with a rotary motion so thatthe center of the cut extends past the center of the bar and is deeperthan the cut at the circumference, and then cutting into the oppositeside of the bar with a rotary motion for a distance such as to meet thefirst center cut but to stop short of the first circumference cut,thereby forming the posts 36 extending between intermediate base 35 andbase 34.

Chamber 37 is gouged out of the steel bar, and all the openingsforsupporting the gear shafts are drilled in alignment through bases 34,35, 38. 7

To assemble the gear shafts in gear cage 26a (FIG. 8), shaft 46 is swunginto chamber 33 and an end thereof is inserted into opening 78. Theother end of shaft 46 is moved into opening 77 so that pinion 47 isreceived in chamber 37 and bearing 75 abuts against the shoulder 81.Bearing 76 is inserted into opening 78 from the other side of base 34aand snap-ring 82 is seated in snap= ring groove 83 to hold the bearingplace. A recess 101 is provided in base 35 to permit the pasage of theend of shaft 46 into chamber 33.

Shaft 43 is swung into position in like manue'ras in dicated by thedot-dash lines in FIG. 8. Bearing 65 and its snap-ring 71 are insertedinto opening 67 from chant-Q ber 37, and bearing 66 and its snap-ring 71are inserted into opening 68 from the motor side of base 34a.

The remaining gear shafts of the gear train are swung into position inchamber 33 in the same manner as shafts 46 and 43, and they aresimilarly supported therein.

Output shaft 51 is provided with a gear 48 which is smaller than theopening 86 so that gear 48 is passed easily therethrough. The small endof shaft 51 is supported by bearing 85 which is seated in opening 87 andabuts against shoulder 88. Bearing 84 is inserted into opening 86 andheld in place by its snap-ring 91 in groove 92.

FIG. 10 illustrates an embodiment of the invention wherein a motor 94 isprovided with two gear heads 102 and 103, each of which is integrallyformed and similar in construction to the previously described gearheads. Gear head 102 is connected to gear head 103 by bolts 104.

Cross shaft 105 extends between chambers 106 and 107. Although gearheads 102 and 103 are connected together with bolts so that there issome chance of misalignment between bases 111 and 112, any suchmisalignment would affect only the cross shaft 105. All the other gearshafts remain in alignment as they should be, and there is no chance ofmisalignment of the two important gears, I

It is to be noted that clearance hole 115 is larger than pinion 116 ofcross shaft 105 so that pinion 116 is easily passed therethrough.

Referring to FIG. 2, gear motor 11 includes outer case 12, stator 13having a stack of laminations 121 and windings 122, identical andinterchangeable bearing plates 14-15 having peripheral flanges 123, 124adjacent the inner surface of case 12 and bearing against the ends oflamination stack 121, cement layer 19 connecting stator 13 to case 12,and rotor 16 supported in the bearing plates 14-15. Bearing plates 14-15have positioning holes 28 formed in peripheral flanges 123, 124, andcase 12 has dimples 31 formed therein in registry with positioning holes28 to join case 12 to the bearing plates 14-15, whereby to properlyposition the elements of the motor 11 relative to each other.

Dimples 31 may initially be half formed so as to snap into holes 28 andthereby properly position the elements, whereupon dimples 31 are furtherdepressed to rigidly connect case 12 to hearing plates 14-15. Ifdesired, holes 28 may be replaced by grooves that encircle the flanges123, 124. Such grooves receive dimples 31 to position the motor elementsaxially.

Referring to FIG. 2a, the bearing plates 14a, 15a may be cemented tocase 12a in a manner similar to that in which stator 13 is cemented tocase 12 by cement layer 19 (FIG. 2), with no dimples 31 or holes 28being used. The procedure in assembling the embodiment of FIG. 2a is to:locate and cement plate 14a in case 12a with a cement layer 126, locateand cement stator 13 to case 12a with a cement layer 19a, and locate andcement plate 15a to case 12a with a cement layer 127. The three piecesmay then be pressed together during the time that the cement is beingcured.

This assembly is then through-bored to assure that the bearing plates14a, 15a, and stator 13 have identical bore diameters and areconcentric. This procedure insures that the later inserted rotor 16and'bearings 17 and 18 are mounted concentrically. Bearing plates 14aand 15a, and stator 13 have been drilled prior to this throughboreoperation, so that the through-bore operation removes only a slightamount of material, just enough to obtain the identical bore on the samecenter for the three elements 13, 14a and 15a.

The gear motor of FIG. 2 is very smallby comparison to previous deviceshaving similar characteristics. It is more compact, its elements havebeen brought closer together, and it is lighter. All of this is, ofcourse, of advantage in miniaturization.

In conventional gear heads using a gear assembly comprising separate endplates joined by bolts, the chances of taking the gear head apart andputting it back together properly are very remote. In the presentinvention, the gear shafts may be removed and replaced in the integralgear cage without any danger of misaligning the gears.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred embodiment. Various changes maybe made in the shape, size and arrangement of parts. For example,equivalent elements may be substituted for those illustrated anddescribed, parts may be reversed, and certain features of the inventionmay be utilized independently of the use of other features, all withoutdeparting from the spirit or scope of the invention as defined in thesubjoined claims.

What is claimed is:

1. A miniature precision electric motor comprising a tubular hollowouter case, a stator having a stack of laminations positioned insidesaid case, a pair of thin bearing plates interchangeable with oneanother and having outer peripheral flanges engaging the inner surfaceof the case over an extensive surface area to rigidly and preciselyretain the plates in given alignment with each other and with the case,said peripheral flanges extending to and bearing against the oppositeends of said lamination stack, said bearing plates each havingcentralized openings and inner flanges about said openings, a pair ofbearings interchangeable with one another and supported by said bearingplates within said openings, said bearings having inner and outer races,locking means for substantially immovably fastening said outer races tosaid bearing plates, a rotor supported by the inner races of saidbearings, and fastening means for rigidly attaching the pe-' ripheralflanges of said bearing plates to the inner surface of said case, saidfastening means comprising dimples formed in one of said case and.flange and positioning holes formed in the other of said case andflanges and in registry with said dimples, whereby the element of saidmotor are properly positioned relative to eachother.

2. In the motor of claim- 1, said outer peripheral flanges of saidbearing plates projecting further into said case than said innerflanges.

3. In the motor of claim 1, said locking means for each bearing platecomprising radially extending openings in said bearing plates andradialprojections from the outer race of said bearings and in registrywith said radially extending openings, and radially expandable lockingrings located in said openingsfor locking said outer race to saidbearing plates.

4. In the motor of claim 1, said bearing plates being identical to oneanother and said bearings being identical to one another. a

5. In the motor of claim 1, a rotor shaft supporting the rotor andhaving an enlarged shoulder bearing against the inner race of eachbearing.

References Cited by the Examiner UNITED STATES PATENTS 2,411,684 11/1946 Hamilton 31042 2,448,500 9/ 1948 Turner 310- 2,819,417 1/1958 Glass3l0-42 2,967,346 1/1961 McMaster 310-42 MILTON O. HIRSHFIELD, PrimaryExaminer.

J. W. GIBBS, Assistant Examiner.

1. A MINIATURE PRECISION ELECTRIC MOTOR COMPRISING A TUBULAR HOLLOWOUTER CASE, A STATOR HAVING A STACK OF LAMINATIONS POSITIONED INSIDESAID CASE, A PAIR OF THIN BEARING PLATES INTERCHANGEABLE WITH ONEANOTHER AND HAVING OUTER PERIPHERAL FLANGES ENGAGING THE INNER SURFACEOF THE CASE OVER AN EXTENSIVE SURFACE AREA TO RIGIDLY AND PRECISELYRETAIN THE PLATES IN GIVEN ALIGNMENT WITH EACH OTHER AND WITH THE CASE,SAID PERIPHERAL FLANGES EXTENDING TO AND BEARING AGAINST THE OPPOSITEENDS OF SAID LAMINATION STACK, SAID BEARING PLATES EACH HAVINGCENTRALIZED OPENINGS AND INNER FLANGES ABOUT SAID OPENINGS, A PAIR OFBEARINGS INTERCHANGEABLE WITH ONE ANOTHER AND SUPPORTED BY SAID BEARINGPLATES WITHIN SAID OPENINGS, SAID BEARINGS HAVING INNER AND OUTER RACES,LOCKING MEANS FOR SUBSTANTIALLY IMMOVABLY FASTENING SAID OUTER RACES TOSAID BEARING PLATES, A ROTOR SUPPORTED BY THE INNER RACES OF SAIDBEARINGS, AND FASTENING MEANS FOR RIGIDLY ATTACHING THE PERIPHERALFLANGES OF SAID BEARING PLATES TO THE INNER SURFACE OF SAID CASE, SAIDFASTENING MEANS COMPRISING DIMPLES FORMED IN ONE OF SAID CASE AND FLANGEAND POSITIONING HOLES FORMED IN THE OTHER OF SAID CASE AND FLANGES ANDIN REGISTRY WITH SAID DIMPLES, WHEREBY THE ELEMENT OF SAID MOTOR AREPROPERLY POSITIONED RELATIVE TO EACH OTHER.